Low-sulfur diesel fuel and use of fatty acid monoalkyl esters as lubricant improvers for low-sulfur diesel fuels

ABSTRACT

The invention relates to a low-sulfur diesel fuel containing a maximum amount of 0.2% by weight of sulfur and fatty acid monoalkyl esters in an amount of between 10 and 50,000 ppm as lubricity improvers, with the fatty acid moieties of the fatty acid monoalkyl esters originating from saturated fatty acids by at least 50%, in particular by at least 70%. It has been shown that said fatty acid esters show a substantially better lubricity improvement in a low-sulfur diesel fuel than a biodiesel made of rape oil and soy bean oil.

This application is a Continuation of co-pending PCT International Application No. PCT/AT2004/000214 filed on Jun. 22, 2004, which designated the United States, and on which priority is claimed under 35 U.S.C. § 120, the entire contents of which are hereby incorporated by reference.

The invention relates to a low-sulfur diesel fuel containing a maximum amount of 0.2% by weight of sulfur and fatty acid monoalkyl esters in an amount of between 10 and 50,000 ppm as lubricity improvers.

Legal provisions enforce a steady decrease in the content of sulfur compounds in mineral fuels. In Europe, the content of sulfur in diesel fuel has been limited to 0.05% by weight since 1996, however, in several countries, e.g. in Sweden, so-called zero-sulfur fuel having a sulfur content of less than 10 ppm is already used almost exclusively today. A so-called city diesel having a content of 50 ppm of sulfur is frequently offered already today especially for use in congested areas.

The elimination of sulfur compounds during refining also involves a deterioration of the lubricating properties of the fuels. It has been possible to show that the elimination of sulfur compounds is also associated with a reduction of polar, oxygenated compounds and polycyclic aromatic compounds which are responsible for the actual lubricity. Reduced lubricity may, however, lead to major damage to the fuel injection pumps of diesel engines. For this reason, it is necessary to add appropriate additives as lubricity improvers to the diesel fuel. Conventional lubricity improvers and additives, respectively, are either synthetic petroleum products or synthetic esters of various chemical structures. As an environmentally friendly alternative, renewable raw materials such as vegetable oils or vegetable oil derivatives such as, e.g., fatty acid monoalkyl esters are today suggested in many cases as lubricating additives.

EP 0 680 506 B describes the use of esters as lubricity improvers.

EP 0 635 558 A1 describes the use of fatty acid monoalkyl esters from saturated and unsaturated fatty acid esters in an amount of from 100 to 10,000 ppm. For this application, especially methyl esters of the composition in which the fatty acids are present in vegetable oils are used without any further pretreatment or separation. A similar application can be learnt from WO 94/17160.

WO 96/07632 describes the production of agents for lubricity improvement by double transesterification of vegetable oils, wherein, in the first stage, fatty acid monoalkyl esters are produced which are transesterified with a polyol in a second stage. Similar compounds are described in EP 1 088 880 A1.

Mixtures of fatty acid esters and dicarboxylic acid esters as lubricity improvers are described in DE 19955354.

U.S. Pat. No. 5,891,203 describes the use of a mixture of biodiesel and diethanolamine derivatives as lubricity improvers in low-sulfur fuels. Hereby, fatty acid amides from diethanolamine and fatty acids are used, wherein especially oleic acid is used as the preferred fatty acid.

In Energy and Fuels (2001, 15, 106-112), the use of biodiesel produced from various raw materials such as sunflower oil, corn oil, olive oil and used edible oils as an additive for lubricity improvement is described, wherein it has been possible to detect a distinct effect with all products, without being able to detect any differences with the individual raw materials.

By means of the directive of the European Commission, the amount of biofuels in the EU is meant to rise to an amount of 5.75% by the year 2010. In order to be able to achieve that amount, it will be necessary especially in the field of biodiesel to fully exploit the potential of possible raw materials. This means that raw materials such as used edible oils, animal fats or palm oil will increasingly have to be used as raw material sources.

A substantial obstacle against using those raw materials as biofuels is the poor low-temperature behaviour of the fatty acid monoalkyl esters produced therefrom, whereby the application as a biodiesel in a 100% form and also as a mixing component is presently still highly restricted.

The present invention starts here, which has as its object to provide an improved low-sulfur diesel fuel having a maximum amount of 0.2% by weight of sulfur, which diesel fuel contains fatty acid monoalkyl esters in an amount of between 10 and 50,000 ppm as lubricity improvers and with which the above-mentioned problem is diminished.

The low-sulfur diesel fuel according to the invention contains a maximum amount of 0.2% by weight of sulfur and fatty acid monoalkyl esters in an amount of between 10 and 50,000 ppm as lubricity improvers and is characterized in that the fatty acid moieties of the fatty acid monoalkyl esters originate from saturated fatty acids by at least 50%, in particular by at least 70%, with the fatty acid monoalkyl esters preferably being provided as fatty acid methyl esters.

The present invention is based on the surprising realization that the lubricating ability of fatty acid monoalkyl esters apparently depends on the content of saturated fatty acid derivatives. For instance, it has been possible to show that fatty acid esters having a content of more than 50% of saturated fatty acids show a substantially higher lubricity improvement in a low-sulfur diesel fuel than a biodiesel made of rape oil or soy bean oil.

Via fractional crystallization and distillation, the amounts of esters comprising unsaturated fatty acids can be separated off. Thus, in particular the fatty acid ester fractions which are obtained by fractional crystallization or distillation and are characterized by a high content of saturated fatty acids are particularly well suited as lubricity improvers.

The fatty acid monoalkyl esters contained in the diesel fuel according to the invention are preferably produced from vegetable fats and/or oils. Possible raw materials are all natural vegetable or animal oils and/or fats whose content of saturated fatty acids already amounts to more than 50%, or corresponding products which were produced by enrichment or separation of the saturated fatty acids from the respective oils and fats. Preferably, appropriate fractions from the processing of palm oil (palm stearin) or animal fat fractions are used.

A further embodiment of the diesel fuel according to the invention is characterized in that it additionally contains one or more additives for improving the cetane number or for improving the low-temperature behaviour.

Furthermore, the invention relates to an agent for improving the lubricity of diesel fuels containing fatty acid monoalkyl esters which is characterized in that the fatty acid moieties of the fatty acid monoatkyl esters originate from saturated fatty acids by at least 50%, in particular by at least 70%.

Furthermore, the invention relates to a process for the production of a fatty acid monoalkyl ester whose fatty acid moieties originate from saturated fatty acids by at least 50%, in particular by at least 70%, which process is characterized in that a fatty acid monoalkyl ester whose fatty acid moieties originate from saturated and unsaturated fatty acids is subjected to fractional crystallization or distillation.

Finally, the invention relates to the use of fatty acid monoalkyl esters as lubricity improvers for low-sulfur diesel fuels, with the fatty acid moieties of the fatty acid monoalkyl esters originating from saturated fatty acids by at least 50%, in particular by at least 70%.

As a measuring method for determining lubricity, the HFRR wear test as per CEC F-06-A-96 was used in accordance with international standards. Here, lubricity is determined by way of the abrasion of a rotating ball. In this method, an abrasion of 460 μm is regarded as the threshold value. The reference fuel used for the tests was a sulfur-free, non-additivated diesel fuel having an abrasion value of 569 μm.

When using different biodiesel samples (made of animal fat, rape oil, soy bean oil and used edible oil), it was surprisingly possible to detect that, when added in an amount of 0.5%, all biodiesel samples did indeed result in an enhancement of lubricating properties but that only by means of the agent according to the invention it was possible to substantially fall below the threshold value of 460 μm. Only when 1.0% was used, the biodiesel samples from rape oil and used edible oil were also able to fall below the threshold value whereas, in case of biodiesel from soy bean oil, even an addition of 2.0% did not result in the threshold value being fallen short of.

Various palm oil samples and palm oil fatty acids, respectively, having high contents of saturated fatty acids were also used for the production of fatty acid methyl esters. All samples had a content of saturated fatty acids of more than 50%. With all samples, it was possible to fall below the threshold value of 460 μm at least when 1.0% was used.

According to European Standard EN 590, an additivation by 5.0% is permitted in a mineral diesel fuel. Since, if additives are used, the price of the additive plays a decisive role and conventional lubricity improvers are available at very low prices, the use of fatty acid alkyl esters is interesting from an economic point of view only if the lowest possible amount of additive is used.

Thus, fatty acid monoalkyl esters having a content of saturated fatty acids of more than 50% constitute ideal additives for improving the lubricating properties of sulfur-free diesel fuels.

By means of the following examples, preferred embodiments of the invention are illustrated further.

EXAMPLE 1

The starting product was an animal fat having the following fatty acid composition:

Lauric acid: 0.2%

Myristic acid: 1.86%

Palmitic acid: 25.17%

Stearic acid: 14.47%

Oleic acid: 42.98%

Linoleic acid: 9.24%

According to known methods, said fat was converted with methanol and potassium hydroxide into the corresponding fatty acid methyl esters. Via fiactional crystallization, the fatty acid methyl esters obtained were separated into two fractions at low temperatures, wherein the fraction having a high content of saturated fatty acids was used as a lubricant additive. The fatty acid composition of said fraction was as follows:

Lauric acid: 2.06%

Myristic acid: 0.44%

Palmitic acid: 33.75%

Stearic acid: 35.00%

Oleic acid: 21.26%

Linoleic acid: 2.62%

Mixtures of said fraction with a non-additivated sulfur-free diesel fuel were produced and the lubricity was determined by evaluating the HFRR wear test as per CEC F-06-A-96.

By way of comparison, different biodiesel samples produced from rape oil, soy bean oil and used edible oil were likewise assessed by the same test. Methyl ester sample 0.5% 1.0% 2.0% Methyl ester from animal fat 443 420 321 after fract. crystallization Rape oil 509 359 320 Used edible oil 521 375 322 Soy bean oil 540 483 487 HFRR abrasion values in μm; reference value of non-additivated fuel: 569 μm Example 2

A technical fatty acid distillate made of palm oil and having the following fatty acid composition was used as a raw material for the production of fatty acid methyl esters:

Myristic acid: 1.59%

Palmitic acid: 52.07%

Stearic acid: 3.93%

Oleic acid: 33.80%

Linoleic acid: 8.37%

Said fatty acid mixture was converted with the aid of methanol and concentrated sulfuric acid as a catalyst, whereby the corresponding fatty acid methyl esters were obtained.

Mixtures of said fatty acid methyl esters with a non-additivated sulfur-free diesel fuel were produced and the lubricity was determined by evaluating the HFRR wear test as per CEC F-06-A-96. Amount of methyl ester 0.5% 1.0% HFRR 426 367 HFRR abrasion values in μm; reference value of non-additivated fuel: 569 μm Example 3

Palm stearin produced by fractional crystallization from palm oil and having the following fatty acid composition was used as a raw material for the production of fatty acid methyl esters:

Myristic acid: 1.3%

Palmitic acid: 73.83%

Stearic acid: 4.84%

Oleic acid: 16.56%

Linoleic acid: 3.52%

With the aid of methanol and potassium hydroxide as a catalyst, palm stearin was subjected to multistage transesterification, whereby the corresponding fatty acid methyl esters were obtained.

Mixtures of said fatty acid methyl esters with a non-additivated sulfur-free diesel fuel were produced and the lubricity was determined by evaluating the HFRR wear test as per CEC F-06-A-96. Amount of methyl ester 0.5% 1.0% HFRR 534 447 HFRR abrasion values in μm; reference value of non-additivated fuel: 569 μm

EXAMPLE 4

Raw palm oil having the following fatty acid composition was used as a raw material for the production of fatty acid methyl esters:

Myristic acid: 1.07%

Palmitic acid: 44.23%

Stearic acid: 4.68%

Oleic acid: 38.28%

Linoleic acid: 11.74%

With the aid of methanol and potassium hydroxide as a catalyst, said palm oil was subjected to multistage transesterification, whereby the corresponding fatty acid methyl esters were obtained.

Mixtures of said fatty acid methyl esters with a non-additivated sulfur-free diesel fuel were produced and the lubricity was determined by evaluating the HFRR wear test as per CEC F-06-A-96. Amount of methyl ester 0.5% 1.0% HFRR 477 456 HFRR abrasion values in μm; reference value of non-additivated fuel: 569 μm 

1. A low-sulfur diesel fuel containing a maximum amount of 0.2% by weight of sulfur and fatty acid monoalkyl esters in an amount of between 10 and 50,000 ppm as lubricity improvers, characterized in that the fatty acid moieties of the fatty acid monoalkyl esters originate from saturated fatty acids by at least 50%, in particular by at least 70%.
 2. A diesel fuel according to claim 1, characterized in that the fatty acid monoalkyl esters are provided as fatty acid methyl esters.
 3. A diesel fuel according to claim 1, characterized in that the fatty acid monoalkyl esters were produced from vegetable fats and/or oils.
 4. A diesel fuel according to claim 1, characterized in that it additionally contains one or more additives for improving the cetane number or for improving the low-temperature behaviour.
 5. An agent for improving the lubricity of diesel fuels containing fatty acid monoalkyl esters, characterized in that the fatty acid moieties of the fatty acid monoalkyl esters originate from saturated fatty acids by at least 50%, in particular by at least 70%.
 6. A process for the production of a fatty acid monoalkyl ester whose fatty acid moieties originate from saturated fatty acids by at least 50%, in particular by at least 70%, characterized in that a fatty acid monoalkyl ester whose fatty acid moieties originate from saturated and unsaturated fatty acids is subjected to fractional crystallization or distillation.
 7. The use of fatty acid monoalkyl esters as lubricity improvers for low-sulfur diesel fuels, characterized in that the fatty acid moieties of the fatty acid monoalkyl esters originate from saturated fatty acids by at least 50%, in particular by at least 70%. 